68 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Tubers of Dioscorea.* — Miss E. Dale describes in detail the structure 

 of the tubers of Dioscorea sativa, which occur both underground and in 

 the axils of the leaves, and which resemble potato-tubers in possessing 

 both " eyes " and adventitious roots. When planted the " eyes " develop 

 stems bearing axillary tubers. The axillary tubers are, in all cases, 

 stem-structures ; and the authoress differs from most previous authorities 

 in regarding the underground tubers of the Dioscoreaceae as also, in 

 most cases, stem-structures. 



Assimilating Roots of Taeniophyllum. f — An examination by J. 

 Midler of the anatomy of the assimilating roots of Taeniophyllum 

 Zollingeri (OrchideeB) leads to the following among the more important 

 results. 



The assimilating organs consist exclusively of dorsiventral aerial 

 roots. The envelope, consisting of two layers of cells, persists only on 

 the ventral side. The exoderm is more strongly developed on the dorsal 

 than on the ventral side, and is, in the former case, exposed. The 

 pneumathode cells are found only on the ventral side. The walls of 

 the ordinary exoderm cells consist of alternate suberified and non- 

 6uberified layers. In older roots the passage of air may be stopped by 

 suberified chlorophyllous wedge-shaped cortical parenchyme cells. 



Besides the ordinary exoderm cells, the pneumathode cells, and those 

 for the passage of air, there occurs in the exoderm a fourth kind of cell. 

 They are very thin-walled dead cells, occurring singly or in large 

 numbers, into which the adjoining cortical parenchyme cells force their 

 way. They have somewhat thickened and suberised walls, are destitute 

 of chlorophyll, and obviously possess the function of checking transpi- 

 ration through the overlying very thin-walled exoderm cells. 



Anatomy of Cassiope.J — Dr. K. Linsbaucr has investigated the 

 anatomical structure of the vegetative organs of Cassiope tetragona, an 

 Arctic representative of the Ericaceae, with the following results. The 

 leaf has on its under side a closed cavity, which is cap-shaped in its 

 upper portion. This cavity is not caused by a rolling up of the margin 

 of the leaf, but by a swelling on all 6ides of a horseshoe-shaped part of 

 the under side of the leaf, and hence from intercalary growth. Tho 

 arrangement of the tissues of the leaf differs materially from that of 

 normal dicotyledonous leaves, especially in the fact that the palisade- 

 parenchyme is formed on the under side of the leaf. 



$. Physiology. 

 (1) Reproduction and Embryology. 



Reduction in the Number of Chromosomes in the Embryo-sac 

 Mother-cell.§ — In a number of Liliifloras examined, J. Schniewind-Thies 

 finds three different types in tho development of the embryo-sac from 

 its mother-cells, viz. : — (1) An embryo-sac mother-cell divides into two 

 daughter-cells ; and these again into four cells, each of which is capable 



• Ann. Bot., xv. (1901) pp. 491-501 (1 pi.), 

 t SB. k. Akad. Wies. Wien, cis. (1900) pp. 667-83 (1 pi.). 

 t Tom. cit., pp. 685-99 (2 pis.). 



§ Die Reduction d. Chroniosrroenzahl u.s.w., Jena, 1901, 34 pp. and 5 pis. See 

 Bot. Ztg., lix. (1901) 2<« Abt., p. 276. 



